音视频同步

音视频有三种同步方式

• 标准时间同步
• 音频时间同步
• 视频时间同步

介绍第一种也是相对简单的一种方式

1. 解码获取已播放时间
2. 根据记录的开始时间和当前时间差值获取实际播放的时间
3. 已播放的时间-实际播放的时间=延迟时间

视频计算

//计算延迟
int64_t pts = av_frame_get_best_effort_timestamp(yuv_frame);
//转换（不同时间基时间转换）
int64_t time = av_rescale_q(pts,stream->time_base,AV_TIME_BASE_Q);
player_wait_for_frame(player,time,player->video_stream_index);

音频计算

int64_t pts = packet->pts;
    if (pts != AV_NOPTS_VALUE) {
            player->audio_clock = av_rescale_q(pts, stream->time_base, AV_TIME_BASE_Q);
    //      av_q2d(stream->time_base) * pts;
            LOGI("player_write_audio - read from pts");
            player_wait_for_frame(player,player->audio_clock + AUDIO_TIME_ADJUST_US, 
            player->audio_stream_index);
        }

延迟计算

/**
 * 获取视频当前播放时间
 */
int64_t player_get_current_video_time(Player *player) {
    int64_t current_time = av_gettime();
    return current_time - player->start_time;
}
/**
 * 延迟
 */
void player_wait_for_frame(Player *player, int64_t stream_time,
        int stream_no) {
    pthread_mutex_lock(&player->mutex);
    for(;;){
        int64_t current_video_time = player_get_current_video_time(player);
        int64_t sleep_time = stream_time - current_video_time;
        if (sleep_time < -300000ll) {
            // 300 ms late
            //这段代码对于300毫秒的处理我也不知道什么意思，拿过来用，有大佬知道什么意思的可以回复一下，不胜感激。
            int64_t new_value = player->start_time - sleep_time;
            LOGI("player_wait_for_frame[%d] correcting %f to %f because late",
                    stream_no, (av_gettime() - player->start_time) / 1000000.0,
                    (av_gettime() - new_value) / 1000000.0);

            player->start_time = new_value;
            pthread_cond_broadcast(&player->cond);
        }

        if (sleep_time <= MIN_SLEEP_TIME_US) {
            // We do not need to wait if time is slower then minimal sleep time
            break;
        }

        if (sleep_time > 500000ll) {
            // if sleep time is bigger then 500ms just sleep this 500ms
            // and check everything again
            sleep_time = 500000ll;
        }
        //等待指定时长
        int timeout_ret = pthread_cond_timeout_np(&player->cond,
                &player->mutex, sleep_time/1000ll);

        // just go further
        LOGI("player_wait_for_frame[%d] finish", stream_no);
    }
    pthread_mutex_unlock(&player->mutex);
}